1. Field of the Invention
The present invention relates to a wireless local area network (WLAN) and, in particular, to a power saving method for WLAN exploiting a novel idle mode operation.
2. Background of the Related Art
Recently, the IEEE 802.11 WLAN standard technology has become a prevailing technology for the broadband wireless Internet access. New applications such as Internet Protocol (IP) telephony are fast emerging today. The IP phones require a functionality to inform the user of sporadic incoming calls even if the user holding a mobile Host (MH) moves around. For the battery-powered IP phone devices, the standby time extension is a key concern for the market acceptance. The current IEEE 802.11 standard based system is not optimized for such an operation. The reason is rooted on IEEE 802.11 WLAN standard, which defines only two operation modes in which a MH can operate, namely, Active mode (AM) and Power Saving mode (PSM). In both modes, since an MH always has to stay connected with one of the access points (APs) even when there is no traffic to/from the MH, it has to perform a handoff at every AP cell boundary. That is, the IEEE 802.11 WLAN is naturally weak in supporting the mobility of MHs when there is no traffic to be served for the MHs.
Due to the lack of such an idle mode operation, both IP paging and PSM have been considered as the alternatives to the Idle Mode (IM) operation. An IP paging technique has been proposed by B. Sarikaya and T. Ozugur, “Tracking Agent Based Paging for Wireless Lans,” in Proc. IEEE CCNC'04, 2004. In this technique, the IP paging supports IP-level mobility when an MH operates in PSM. The proposed IP paging does not support an efficient power consumption for an MH since both IP level paging and PSM operate so independently that IP paging has nothing to do with a PSM. For a longer standby time when adopting the IP paging, more suitable power saving schemes other than PSM needs to be considered.
Other IP paging schemes have been proposed by X. Zhan, J. Gomez, G. Castellanos, and A. T. Campbell, “P-MIP: Paging Extensions for Mobile IP,” ACM Mobile Networks and Applications, July 2002, and by R. Ramjee, L. Li, T. La Porta, and Sneha Kasera, “IP Paging Service for Mobile Hosts,” in Proc. ACM MobiCom'01, 2001. If there is no Media Access Control (MAC) level paging scheme, IP paging could be used as an alternative. However, because the original IP-paging concept was developed to support the mobility for IP layer regardless of MAC layer, these IP paging schemes deal with only IP-paging algorithms and ignore MAC operation under the assumption that the MAC of an idle mode operates in an efficient power saving manner. In the case of the IEEE 802.11 WLAN standard, the MAC operates in the PSM when utilizing the IP paging. The MH in PSM, while running the IP paging, is not able to fall into idle state properly since the MH has to perform necessary operations in order to maintain the connection with an AP and perform IP paging-related operations. “Wake On Wireless: An Event Driven Energy Saving Strategy for Battery Operated Devices”, E. Shih, P. Bahl, and M. J. Sinclair, in Proc. ACM MobiCom'02, 2002 discloses a good example of power saving by adopting the paging concept. In this power-saving technique a practical device having ability to receive paging signals is developed, and the device wakes up an idle MH when a packet destined to the MH exists. The device for paging works so well that the MH with the device achieves longer standby time. However, this power saving technique is not standard compliant.